Preliminary studies from our laboratory suggest that Parkinson patients may demonstrate a significantly diminished emotional reactivity to fear-inducing emotional materials compared to their healthy counterparts. This may be related to the fact that the amygdala has been shown to exhibit pathology in Parkinson's disease (PD), and is a neural structure that plays a key role in processing and interpreting signals of threat in the environment. As such, the proposed study will test the following hypotheses: a) Parkinson patients will demonstrate reduced emotional reactivity, as indexed by emotional modulation of startle, to both verbal and nonverbal fear-inducing stimuli; b) emotional reactivity to fear inducing materials will correlate with amygdala volume; and c) reduced emotional reactivity will correlate with an increased propensity for families to inaccurately view their Parkinson family member as depressed and unmotivated. These hypotheses will be tested through a method that is not confounded by deficits of overt expression in PD: emotional modulation of the startle eyeblink reflex. Increased understanding of emotional changes accompanying PD may prove to be clinically useful by reducing problems such as healthcare worker and family member misattributions that the Parkinson patient is "uninterested" or depressed due to lack of reaction. This proposal will also examine 1 potential neural mechanism for reduced emotional reactivity in PD, decreased amygdala volume, with the aim of increasing knowledge of neuropathological changes that may lead to emotional reactivity deficits in PD.